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grep -oE '[a-z]+' words.txt | sort | uniq -c | sort -nr | awk '{print $2" "$1}' 
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tr -s ' ' '\n' < words.txt | sort | uniq -c | sort -nr | awk '{print $2, $1}'
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awk '{
    for (i = 1; i <= NF; ++i) ++s[$i];
} END {
    for (i in s) print i, s[i];
}' words.txt | sort -nr -k 2